As having the advantages of impact resistance, heat resistance and good electric properties, polycarbonate resins have many applications in various fields of, for example, OA (office automation) appliances, information and communication appliances, other electric and electronic appliances for industrial use and household use, automobile parts and building materials. As a rule, polycarbonate resins are self-extinguishable. However, some fields of typically OA appliances, information and communication appliances, and other electric and electronic appliances for industrial use and household use require high flame retardancy, for which are used various flame retardants to improve their flame retardancy.
For improving the flame retardancy of polycarbonate resins, halogen-containing flame retardants such as bisphenol A halides and halogenated polycarbonate oligomers have been used along with a flame retardation promoter such as antimony oxide, as their flame-retarding ability is good. However, with the recent tendency toward safety living and environmental protection from discarded and incinerated wastes, the market requires flame retardation with non-halogen flame retardants. As non-halogen flame retardants, phosphorus-containing organic flame retardants, especially organic phosphate compounds may be added to polycarbonate resin compositions, for which various methods have been proposed. Such flame retardants, organic phosphate compounds serve also as a plasticizer, and polycarbonate resin compositions containing them exhibit excellent flame retardancy.
In order to make polycarbonate resins have good flame retardancy by adding thereto a phosphate compound, a relatively large amount of the compound must be added to the resins. In general, polycarbonate resins require relatively high molding temperatures, and their melt viscosity is high. Therefore, for molding them into thin-walled and large-sized moldings, the molding temperature will have to be more and more higher. For these reasons, phosphate compounds often cause some problems when added to such polycarbonate resins, though their flame-retarding ability is good. For example, phosphate compounds often corrode molds used for molding resins containing them, and generate gas to have some unfavorable influences on the working environments and even on the appearance of the moldings. Another problem with phosphate compounds is that, when the moldings containing them are left under heat or in high-temperature and high-humidity conditions, the compounds lower the impact strength of the moldings and yellow the moldings. On the other hand, the recent tendency in the art is toward recycling resin products for saving natural resources. However, as not stable under heat, phosphate compounds are against the requirement for recycling resin products containing them. This is still another problem with phosphate compounds.
Apart from the above, known is another technique of adding silicone compounds to polycarbonate resins to make the resins have flame retardancy. In this, silicone compounds do not give toxic gas when fired. For example, (1) Japanese Patent Laid-Open No. 139964/1998 discloses a flame retardant that comprises a silicone resin having a specific structure and a specific molecular weight.
(2) Japanese Patent Laid-Open Nos. 45160/1976, 318069/1989, 306265/1994, 12868/1996, 295796/1996, and Japanese Patent Publication No. 48947/1991 disclose silicone-containing flame-retardant polycarbonate resins. However, the level of the flame retardant disclosed in (1) is high in some degree, but the impact resistance of resin moldings containing it is often low. The technology of (2) differs from that of (1) in that the silicones used in (2) do not act as a flame retardant by themselves, but are for improving the dropping resistance of resins, and some examples of silicones for that purpose are mentioned. Anyhow, in (2), the resins indispensably require an additional flame retardant of, for example, phosphate compounds or salts of Group 2 metals. Another problem with the resins described in (2) is that the flame retardant added thereto worsens the moldability of the resins and the physical properties of the resin moldings.
Also known is a flame-retardant polycarbonate resin composition that comprises a polycarbonate-polyorganosiloxane copolymer-containing resin (this is one type of polycarbonate resin) and contains a fibril-forming polytetrafluoroethylene (Japanese Patent Laid-Open No. 81620/1996). Even though its polyorganosiloxane content is low, falling within a defined range, the composition exhibits good flame retardancy. Japanese Patent Laid-Open No. 176425/1996 discloses a method of using an organic alkali metal or alkaline earth metal salt and a polyorganosiloxane for improving the flame retardancy of polycarbonate resins without detracting from the transparency thereof. In the two known techniques, however, the flame retardancy of the resin compositions could be improved, but the impact resistance thereof is often lowered.
Japanese Patent Publication No. 70176/1994 discloses a method of using a core/shell type elastomer as one component of polycarbonate resin compositions, in which the elastomer is for improving the flame retardancy of the resin compositions not detracting from the impact resistance thereof. However, this is still problematic in the thermal stability of the resin compositions. When the resin compositions are molded into large-sized moldings, they are often yellowed or silvered and therefore their appearance is not good.
The present invention has been made in the current situation as above, and its object is to provide a non-halogen (other than fluorine), flame-retardant polycarbonate resin composition of which the flame retardancy is good and which has good moldability, good impact resistance, good thermal stability, good wet heat resistance and good recyclability.